Stack Effect

This is a naturally-occurring phenomenon of vertical structures where the building heats air which then rises and escapes through the top of the building. This creates a vacuum which draws new air in the bottom. Thus, air continues to come in the bottom of the building, and circulate out the top.

This is very problematic in the case of high-rise fires. As the fire heats the air, the air escapes upward, drawing new air in below the fire to feed it, and creating an artificial wind which pushes the fire up the building.

Occasionally, in very hot climates, you get a “reverse stack effect” where the air conditioning in the building cools the outside air, lowering its temperature, and causing it to settle and come out the bottom.

This phenomenon is the basis for things like solar chimneys and solar updraft towers.

Why I Looked It Up

This came up in a book about skyscraper construction. It’s a huge design consideration, apparently.

Also, it immediately got me thinking about shower curtains. I had always known that shower curtains tend to blow inwards at the bottom when taking a shower. I thought that this is because the hot water heated the air, which essentially caused (what I now know to be) a stack effect inside the shower.

However, the Wikipedia page on Shower-Curtain Effect states that this likely isn’t so, since apparently it still happens when cold water is used (I don’t take many cold showers). The page says the phenomenon is not totally understood, but the Bernoulli Principle is the most accepted explanation. It theorizes that the water coming out of the shower head accelerates the air it travels through, which lowers its pressure.

Postscript

Added on January 11, 2021

This article discusses a deadly fire in the Bronx. Two Open Doors Created ‘Flue Effect’ of Deadly Smoke at Bronx High-Rise. It uses the phrase “flue effect,” but it’s basically the same thing:

As the fire burned, the smoke was drawn through the broken door on the third floor toward an open stairwell door high above on the 15th floor.

“If you have that door on the upper floors open, that’s really going to give you a flue effect, like a chimney, and that’s what occurred,” said Jim Long, a spokesman for the Fire Department.

[…] Smoke spread quickly into the hallway and then into the building’s internal stairwells, the main means for residents to evacuate. Commissioner Nigro said that another door was also left open to the stairwell on the 15th floor, pulling “dangerous” fumes up through the building. He noted that the 15th floor in particular “became quite untenable.””

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